Frequency responsive measuring and controlling apparatus



Dec. 26, 1950 R. F. WILD 2,535,248

FREQUENCY RESPONSIVE MEASURING AND CONTROLLING APPARATUS Filed July 29, 1944 7 Sheets-Sheet 1 FIG. I

OSCILLATOR .POWER SUPPLY OSCILLATOR FREQUENCY MIXER DISCRIMINATOR VOLTAGE AMP.

POWER AMP.

0.61 POWER SUPPLY INVENTOR. RUOOLF F. WILD ATTOR Y.

Dec. 26, 1950 Y CONTROLLING APPARATUS Filed July 29, 1944 R. F. WILD FREQUENCY RESPONSIVE MEASURING AND 7 Sheets-Sheet 2 TRANSMITTER RECEIVER 10 ,u l2 i I 1 OSCILLATO; FREQUENCY BALANCED 7 "MR BUFFER FREQUENCY "l f DISCR'MINATORO- L 1 5 T T G G G a G G F "0.0. Pow R SUPPLYE r.

OSCILLATOR 8 4 KEYER s L* I 1 G FIGZ 86 o.c POWER I, SUPPLY POWER AMP. VOLTAGE AMP \IN V EN TOR.

RUDOLF F. WILD TTOR Y.

Dec. 26, 1950 R. F. WILD FREQUENCY RESPONSIVE MEASURING AND CONTROLLING APPARATUS '7 Sheets-Sheet 3 Filed July 29, 1944 INVENTOR. RUDOLF F. WILD Ji mm.

ATTORNEY.

Dec. 26, 1950 Filed July 29, 1944 WILD FREQUENCY RESPONSIVE MEASURING AND CONTROLLING APPARATUS TRANSMITTER 7 Sheets-Sheet 4 6 (IO l OSCILLATOR RECEIVER I l T T BALANCED FREOUENGY M'XER FREQUENCY Fl J -DlSCRlMlNATORo- L 1 T T 5a I 0 G G G A.C.POWER SUPPLY 8 QSCILLATOR L 'G T 6 107 o.c. PowER /8a ,I SUPPLY I6 I4 L POWER AMP. VOLTAGE me L' TRANSMITTER i 4 6 2 OSCILLATOR L as RECEIVER. l l r O T I I 4 T FREQUENCY 'rg M'XER JNSCRIMINATORQ- 1 l. 1 D G s c e 0.0. POWER 2 SUPPLY 8 \OSCILLATOR 7- T 9 A.C.POWER 8L SUPPLY 2 POWER AMP. VOLTAGE AME INVENTOR. RUDOLF F. WILD ATTOR Y.

R. F. WILD FREQUENCY RESPONSIVE MEASURING AND CONTROLLING APPARATUS Dec. 26, 1950 7 Sheets-Sheet 5 Filed July 29, 1944 I mmvrox. RUOOLF F. wu o ATTOR Dec. 26, 1950 'R. F. WILD FREQUENCY RESPONSIVE MEASURING AND CONTROLLING APPARATUS '7 Sheets-Sheet 6 Filed July 29, 1944 INVENTOR. RUDOLF F. WILD ATTORNEY.

Dec. 26, 1950 R. F. WILD 2,535,243

FREQUENCY RESPONSIVE MEASURING AND CONTROLLING APPARATUS Filed July 29, 1944 7 Sheets-Sheet 7 TRANSMITTER RECEIVER lo l2 4\ -z z E 7 BALANCED OSCILLATOR Jfiiigg FREQUENCY D *1 I, l DISCRIMINATOR..

l -sa c *c; s a

h i 1 .A.C.POWER SUPPLY '0sc||.LAToR' a 5 9 G 0 I 6/? 1 FIG ll A.C. PowER 8b SUPPLY I6 I41 4 4 4 POWER AMP. VOLTAGE AM.

INVENTOR.

RUDOLF F. WILD BY gfM ATTOR EY.

Patented Dec. 26, 1950 FREQUENCY RESPONSIVE MEASURING AND CONTROLLING APPARATUS Rudolf r. was, Philadelphia, 'Pa., assignor, by mesne assignments, to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application July 29, 1944, Serial No. 547,253

14 Claims.

I 1 The present invention relates to measuring and controlling apparatus and more particularly to electrical apparatus for measuring, indicating, recording and/or controlling variable conditions such as temperature, pressure, liquid level and flow and also has utility for telemetering, torque amplifying, boat steering, remote control and repeater positioning purposes.

A general object of the invention is to provide improved electrical apparatus of the above mentioned character.

In my copending application Serial No. 537,505, filed on May 26, 1944, I have disclosed and claimed various apparatus embodiments of an electrical measuring and controlling apparatus of the above mentioned type. These apparatus embodiments are characterized in that they comprise tunable means including in combination an oscillator which generates a relatively high frequency oscillating current, means to amplitude modulate the high frequency current at the frequency of oscillation of a relatively low frequency current, balanced high frequency discriminating means responsive to the frequency of the modulated high frequency current and operative to create a signal voltage oscillating at the low frequency and of one phase or of opposite phase and having a magnitude depending respectively upon the direction and extent of the deviation of frequency of oscillation of the high frequency current from a predetermined value, and phase responsive motive structure controlled by the derived oscillating signal voltage.- The pha e responsive motive structure is employed to adjust the frequency of oscillation of the high frequency'current, or alternatively the frequency value to which the discriminator rreans is tuned, as required to reduceto zero the low frequency oscillating signal voltage and thereby to rebalance the apparatus. The alternative rebalancing ad ustment referred to, namely adjustment of the frequency value to which the frequency discriminator is tuned, has particular utility in telemeterlng and analogous apparatus in which the oscillator and its detuning means are remotely located with respect to the frequency discriminating means and the rebalancing motive structure.

In a later filed copending a plication Serial No. 543,892, filed on July 7, 1944, now Patent No. 2,4Q4,344, I have disclosed and claimed other apparatus embodiments of an electricalmeasuring and controlling apparatus of the type described above having particular utility for telemetering and analogous purposes and wherein the reba c s djustments of h p tus a e ac- 2 complished independently of adjustment of th frequency value to which the discriminating means is tuned. Instead, a second oscillating signal voltage of the low frequency is locally generated at the receiver and mixed with the first oscillating signal voltage of low frequency to produce a resulting oscillating signal of said low frequency and of one phase or of opposite phase accordingly as the amplitude of the first oscillating signal voltage is greater or less than the second oscillating signal voltage. This resulting oscillating voltage is utilized to control the actuation of the phase responsive motive structure and the latter in turn is employed to vary the amplitude of oscillation of the second oscillating signal voltage. It is noted that in an apparatus of this type the balance of the apparatus depends upon both the phase and the amplitudes of two oscillating. signal voltages or, stated differently, on two types of variables.

The present invention is directed to improvements in electrical measuring and controlling apparatus of the same general character as those di closed in my above mentioned copending applications and is especially advantageous for telemetering and analogous purpwes in that the rebalancing operations are accomplished independently of the frequency value to which the frequency discriminating means is tuned, and furthermore, the balance depends upon only one type of variable, namely, the frequencies of the two high frequency oscillating currents. The provision of such an arrangement forms a pri ary object of the pre ent invention.

In particular, the arrangement of the present invention includes a transmitter comprising an oscillator for generatin a high frequency oscillating current of substantially constant amplitude and of a frequency which varies in accordance with the effect to be indicated at a remote point. This effect may be some variable condition such as rate of flow, temperature, pressure, or the po ition of an elementsuch as a pointer or the like. To this end the transmitter oscillator may desirably include a tunable circuit compri ing an inductance element and a variable condenser connected in parallel relation, the condenser being adaptedv to have its capacity varied in accordance with the effect to' be remotely indicated. For indicating the effect, there is provided a receiver which may be located at a point remote from the transmitter and connected thereto by means of a transmission line. If desired, wireless transmission-may also be employed.

The receiver includes a local oscillator for generating a high frequency oscillating current of substantially constant amplitude and of variable frequency. In addition, a frequency mixer is provided for heterodyning the received high frequency oscillating currents received from the transmitter oscillator and from the local receiver oscillator. In one embodiment of the present invention the resulting oscillating current obtained from the frequency mixer is applied to a buffer tube which is made substantially non-conducting by means of keying or amplitude modulatlng means at regularly recurring intervals of a relatively low frequency which, merely by way of example. may be 80 cycles per second. The keyed or amplitude modulated oscillating output current from the buffer tube is applied to a balanced frequency discriminator which, in the balanced condition of the apparatus. may be tuned either to the sum or to the difference of the frequencies of the transmitter and receiver oscillators.

For deriving a reversible motor drive from the discriminator output voltage there are provided a voltage amplifier, a power amplifier and a twophase rotating field induction motor as disclosed in my aforementioned copending applications. The local receiver oscillator is provided with a retuning element such as a. variable condenser which is mechanically coupled to the motor shaft. When the apparatus is in balance, the sum or difference of the signal frequencies of the transmitter and receiver oscillators is equal to the balanced frequency of the discrimin tor. Upon change in the frequency of the oscillating current output of the transmitter oscillator, due, for example, to a change in the effect to be remotely indicated, the sum or difference of the oscillator frequencies is correspondingly changed. As a consequ nce, the discriminator produce an output signal voltage undulating at said relatively low frequency and of one phase or of o posite phase depending upon the direction of the change, which discriminator output signal volta e is operative to effect energization of the reversible motor in the proper direction to vary the capacity of the tuning condenser of the local oscillator as required to restore the sum or difference of the transmitter and receiver oscillator frequencies to the value to which the discriminator is tuned.

By properly shaping the rotor plates of the tuning condens rs of t e transmitter and receiver oscillators, it is possible to cause the position of the rotor of the tuning condenser of the receiver oscillator to assume any desired positional relationship with respect to the variable effect in accordance with which the transmitter oscillator tuning condenser is varied. For example, if the transmitter oscillator tuning condenser is varied by a differential pressure indicative of the rate of flow of a fluid through a pipe, the position of a pointer coupled to the tuning condenser of the receiver oscillator and the motor shaft may be made to indicate in a linear manner the rate of flow of the fluid through the pipe even though the differential prasure does not vary linearly with respect to said rate of flow.

In other embodiments of the invention which are disclosed, the amplitude modulating or keying means for causing the voltage output of the frequency discriminator to undulate at the relatively low frequency is dispensed with and such keying or amplitude modulation is obtained by means of direct keying of the transmitter and/or receiver oscillators. Thus, in one embodiment. the transmitter oscillator may be provided with an alternating aode voltage supply so that high frequency oscillating currents are created by the transmitter oscillator only during regularly recurring intervals of the low frequency of 'the alternating anode supply voltage. With this embodiment the balanced frequency discriminator is so designed that its balanced frequency is equal to the sum or difference of the frequencies of the transmitter and receiver oscillators during the intervals when the transmitter oscillator is operative. During the alternate intervals when the transmitter oscillator is not producing high frequency oscillating current, only high frequency currents from the receiver oscillator are impressed on the frequency discriminator. The frequency discriminator is so designed, however, that it is substantially non-responsive to oscillating currents of that frequency. As a result, zero output voltage is produced by the discriminator during such non-operative intervals of the transmitter oscillator and also during the intervals when the frequency of the resulting oscillating current output of the frequency mixer is the value to which the discriminator is tuned. Upon change in the frequency of oscillation of the transmitter high frequency current, however, an undulating voltage of the low frequency of the alternating anode supply voltage for the transmitter oscillator is created at the output terminals of the frequency discriminator. That undulating voltage is of one phase or of opposite phase depending upon the direction of the change and is utilized to control the selective energization of the reversible drive means to effect a corres onding change in the frequency of oscillation of the local receiver oscillator thereby to rebalance the apparatus.

In another embodiment of the invention which has been disclos d, the keyin or amplitude modulation is accom lished by providing an alternating anode voltage su ply for t e local receiver oscillator. The manner of operation of this embodim nt of my invention is substanti lly identical to that just described in which the transmitter oscillator is p ovided with an alternating anode voltage sup ly.

In a f rth r embodiment of the invention both the transm tt r and the receiver oscillators are provided with alternatin anode voltage supply means so that both oscillators are operative to create hi h frequency oscillating currents only during concurrent and regularly recurring intervals. With t is arrang ment both o cill tors preferably should be en r ized by a common alterhating curr nt sup l line, or the alternating current supplied by individ"al supply lines should be ap roxi at ly in phase. According to this embodiment, when the a paratus is balanced. the sum or difference of the frequency of the t ansmitter and receiver oscillators is the frequency value to which the frequency discriminator is tun d, and therefore, zero output voltage is obtained from the frequency discriminator. During the alternate half cycles of the alternating anode volta e supplied to the transmitter and receiver oscillators when the latter are not operative to create high frequency oscillating currents, n oscillating currents are applied to t e input circuit of the frequency discriminator, and therefore, zero output voltage is obtained from the discriminator. Upon change in the frequency of the high frequency current output from the transmitter oscillator, however, the sum or difference of the transmitter and receiver oscillator frequencies produced during the operative half cycles is changed.: and consequently, the disupon'the direction of change. This undulating discriminator outputvoltage is utilized to control theselective actuation of the reversible drive means in the propendire'ction. to effect a c responding change in thefrequency of oscillationof the high frequency current output ofthe receiver oscillator thereby'to restore the frequency ofoscillatiom of the current applied to the discriminator to the value to which'the' latter is tuned. and hence, to rebalance the apparatus.

{Theyarious features of novelty whichfcharacterize myinvention are pointedout with particularity in the claims annexed toand' forming a partof this specification. For a better understandingof the invention, however, its advantages andspecificobiects obtained with its use, reference should behad to the accompanying drawings and descriptive matter in which are illustrated and described preferred embodiments of the invention. f the dr wings: l is diagrammatic illustration of one embodiment of the invention:

Fig.. 2 is a block diagram illustrating the electrical circuit arrangement of the apparatus of Fig. l;

Fig. 3' illustrates in detail the electrical circuit components of the circuit arrangement of the block diagram of Fig. 2; 7

Figs. 4, 5 and 6 are graphsillustrating the operation of the frequency discriminator of the circuit diagram of Fig. 3;

Fig. 7 is a'block diagram illustrating a modification of the electrical circuitarrangement of theapparatusof Fig. 1: 1

Fig. ,8 is a detailed wiring diagram illustrating the electrical circuit components 01 the block diagram of Fig. 7;

Fig. '9 is a block diagram illustrating a further modification of the electrical circuit arrangement of the apparatus of Fig. l;

Fig. 10 is a wiring diagram illustrating in detail the electrical circuit components of the block diagram of Fig. 9; and

Fig. 11 is a block diagram illustrating a still further modification of the electrical circuit arrangement of the apparatus of Fig. 1.

In Fig.1 I have illustrated, in a more or less diagrammatic manner, a measuring, indicating, recording and controlling apparatus for measuring, indicating, recording and controlling the rate of flow of a fluid through a pi e or a conduit I. The rate of flow of fluid through the pipe I is detected by a-manometer, which is designated at 2, and is arranged to operate a variable tun-' ing condenser, desi nated by the numeral 3, for detuning a resonant electrical circuit comprising the frequency determining circuit of a high frequency oscillator l. The high frequency oscillator-l is utilized as a generator and transmitter of high frequency oscillations and is provided with direct current power su ply means 5, as shown in Fig. 2. The high frequency current output derived from the oscillator 4 is of variable frequ ncy dependent upon the adjustment of the variable tuningcondenser 3, and is conveyed by-means of a transmission line, which may comprise a coaxial cable 6, to a receiver which has been designat d by the reference numeral I. If desired, matchingstages or amplifiers may be add d at, both ends ofv the transmission line, or means for wir less transmission may be provided in the. conventional manner.

The receiver 1, shown lnjthelblock diagram of. Fig.'2, comprises a local oscillator indicated at land provided with a D.,C,. ,power supply v means 8. for generating, a .high frequency oscil- 'lating current of substantially constant amplitude and of variable frequency depending upon the adjustment of a variabletuning condenser 9 which is connected in the frequency-determining circuitofthe oscillator;8. A frequency mixer; indicatedat' l0, is proyided for heterodyning the received high frequency oscillating currentsirdm thetransmitte'r oscillator l, and the {high frequency currents fromv the receiver os- I cillator 8. The resulting oscillating currentoutput from the frequency mixer I0 is applied to a buffer, indicated at H, which is periodically made non-conducting-fby means of a keyer, indicated at l3. As shown in. Fig.3, the keyer I3 is supplied with energizingcurrent from supply lines L and L', which supply alternating current having a relatively 'low frequency of 60 cycles per second, Consequently, theoscillating. current output from thebufler II is keyed or amplitude modulatedat 60 cycles per second. This oscillating current output is applied to a balanced frequency discriminator, indicated at l2, which may be tuned either to the sum or difference of the frequencies of the transmitter oscillator I and the receiver oscillator 8 in the'balanced condition vof the apparatus. Merely for purposes of illustration and example, the frequency discriminator I! may be assumed .to be tuned to the difference of the frequencies of the transmitter and receiver oscillating. currents. When they frequency of the oscillating current output of the transmitter oscillator 4 is changed as a result of adjustment of the detuning condenser 3, the difference between the transmitterand receiver oscillator discriminator undulating output voltage, there is provided a voltage amplifier [4, a power amplifier l6, and a reversible electrical motor indicated'at i 5. Thus, the undulating voltage output is am lified by the voltage amplifier I4 and the amplified quantity is applied .to the power amplifier 16 which, in turn, operates under control of said amplified quantityto energize selectively the motor l5 for rotation in one direction or the other according to the phase of the un-v dulating voltage, and hence, according to the direction of change of frequency .of the high fre: quency current oscillations of the transmitter oscillator 4. The shaft of the motor I5 is mechanically coupled to the tuning condenser 9 connect d inthe frequency det rmining cir: cuit of the receiver oscillator 8 and its operation is employed to vary the capacity of thetuning condenser 9 as required to restore the difference of the frequencies of the transmitter and receiver oscillations to the frequency value to which th discriminator I2 is tuned. I

Merely by way of example, the balanced frequency of the frequency discriminator l2 may be made 4"-0 kilocy les and the frequency of oscilla-. tion of the high frequency current'output from the transmitter oscillator may be varied between 1460 kilocycles and 1000 kilocycles, while the frequency of the oscillating current output of the receiver oscillator I is simultaneously adjusted by means of the operation of motor II to the proper frequency between 1000 and 560 kiloeycies so that the diflerence between the transmitter of receiver oscillator frequencies is always maintained at 450 kilocycles. v

Aamaybeseenbyreferencetol'iss.1and8. the motor I! is a two-phase induction motor of the rotating fleld type. In addition to operating the retuning condenser I of the receiver oscillator I, the motor II is also arranged to operate indicating and recording mechanism generally designated at i1 and control apparatus shown at "a which, in turn, operates controlling means designated at llb for controlling the flow of fluid through the pipe I.

The manometer 2 for the rate of fluid flow through the pipe I may be of any known type and, as shown, includes an oriflce plate it which is positioned in the pipe I for creating a pressure differential across the oriflce plate II which varies in accordance with the rate of fluid flow through the pipe. The pressure differential so produced is a square function of the rate of flow through the pipe I. Manometer 2 also includes a high pressure chamber is which is connected by tube 20 to the high pressure side of the orifice plate ll andincludes a low pressure chamber 2! which is connected by a tube "to the low pressure side of the oriflce plate II. The low pressure chamber 2i and the high pres ure chamber ll communicate with each other through a tube II.

The relative levels of mercury or other suitable liquid located within the pressure chambers I and II vary in accordance with the pressure dif-- ference within those chambers, and consequently, provide a measure of the rate of fluid flow through the pipe I. A member 24 which floats on the mercury in the high pressure chamber i0, and therefore rises and falls in accordance with variationslnpressure diflerential in the two chambers II and II, is arranged to deflect angu-,

tuning condenser 8. The variable condenser 3' comprises movable condenser plates 21 which are deflected relatively to stationary condenser plates 2! upon angular deflection of the gear sector 2!. By way of example, an increase in the rate of fluid flow through the pipe i may be assumed to cause the condenser plates 21 to rotate in a clockwise direction to decrease the capacity between the condenser plates 21 and 28.

As shown in Fig. 1, the reversible electrical motor It includes a stator "and a squirrel cage rotor which is provided with suitable conductor bars. As tho e skilled in the art will understand, the rotor 30, if desired, may comprise a rotatable cup composed of copper or aluminum. Such a rotor is desirable in applications wherein a low inertia rotor is required. A power winding II and a control winding 32 are wrapped around suitable pole pieces provided on the stator 2!. Depending upon the phase relation of the electrical current flowing through the control winding 82 with respect to the current flowing through the power winding 3i, as is more fully explained hereinafter, the rotor is actuated for rotation in one direction or the other to cause rotation of a pinion gear 83 in a corresponding direction.

The pinion gear it drives a gear 84 which is carried by a shaft 35 and is provided with a proiec tion 20 which abuts against the pinion gear 03 for the purpose of limiting the extent of rotation of the gear It.

Gear 34 carries a cable drum 81 which operates a cable 38 over pulleys :9, 4|, ti and l2.

The pulley 39 is carried by a lever 43 which is biased by a spring 44 in a clockwise direction about the pivot point 4! of the lever to maintain the cable ll taut. The pulley 42 is arranged to operate the retuning means or variable tuning condenser 0' which, as seen in Fig. 1, comprises a variable condenser having movable condenser plates 40 adapted to be rotated with respect to relatively stationary condenser plates 01 upon rotation of the pulley 42. The retuning means I, therefore, is adjusted in accordance with the angular positions assumed by the rotor II of the motor ll.

Shaft II which carries the gear is also operates an indicating pointer (not shown) with respect to a suitable calibrated indicating scale, also not shown. Also mounted on the shaft 80 is a gear it which meshes with a gear sector It so that upon rotation of the motor I! the gear sector 4.! is rotated about its pivot 50. The gear sector is positions a pen arm 5| with respect to a slowly rotating chart 52 for the purpose of providlng a continuous record of the rate of fluid flow through the pipe i on the chart '2. Chart 02 is driven at a constant slow speed by a unidirectional synchronous motor which, as shown in Fig. 3, is supplied with alternating energizing current from supply lines L and L" through a switch 54. The gear sector It also operates an arm 55 which is arranged to adjust the position of the flapper of a neumatic control device It forming a part of the control apparatus Ho. The pneumatic control device It may be of the type shown and described in Patent No. 2,125 081 which was issued to C. B. Moore on July 26, 1938, and includes a nozzle valve which is disposed in cooperative relation to the flapper and is connected by a bleed line I1 to a pilot valve 58 su plied with air under pressure by a pipe 59. The pressures developed by the pilot valve II are transmitted through a pipe 60 to the pneumatic control device It and by a pipe ii to a pneumatic motor 62 in the control means "b for controlling the rate of fluid flow through the pipe i. The pneumatic control apparatus inclndim the control device 50. the pilot valve SI and the control means llb may advantageously be utilized for the purpose of maintaining the rate of fluid flow through the pipe I at a sub tantiall constant value.

The details of construction of the reversible moto II, the indicating and recording apparatus I1 and the pneumatic control apparatus l'lo and "b are completely illustrated and described in a copending a plication of Walter P. Wills, Serial No. 421,173, filed on December 1, 1941, which issued as Patent No. 2,423,540 on July 8. 1947. Therefore, further disclosure thereof is not considered necessary herein.

The electrical circuit arrangement of the transmitter and receiving apparatus of my present invention, shown in more or less diagrammatic manner in the block diagram of Fig. 2, is illustrated in more detail in Fig. 3 wherein are shown the various electrical components comprising the various units of the block diagram of Pig. 2.

Transmitter oscillator I as shown in Pig. 8

is an electron coupled oscillator. and includes a pentode tube 83 which may be of the commercially available ty e ssJ'zi 'r ne n includes an anode 84; a suppressor-grid 85 asc'reen grid 88,

a control grid 81; a cathode '88 andja heater illament 89. The heater filament 89 is connected to-and receives energizing; current fr'omthe secondary winding'10of'a transformer 'lI having a ,assaasa circuit which may be traced from the positive outjut terminal of the filter 83 through. resistance BLSCI'BSI] grid 88, cathodei88, inductance coil 18 and ground G to the negative terminalgof the filter 83. These control'grld andscreen grid circuits are inductively coupled by the inductance coils vI8 and 19 and provide for high frequency operation within asuitable; range of frequencies line'voltage primary windingi12, a'high'v voltage secondary winding 13 and 'alow'voltag'e secondternating current which supplies alternating currentof relatively low frequency, for example, 60

' cycles per second, although it will be understood that other frequencies of alternation may be employed equally as well; The transformer H is contained in andcomprisesa part of the D. C. power supply means 8 for the t'ransmitter oscillator4.

Control grid 81 of the pentode tube 83 is connected through a resistance 18 to ground (3 and is also connected through a condenser 11 to one terminal of a parallel circuit including the variable condenser 3 in one branch and an inductance coil 18 in the other branch. The inductance 'coil 18 is inductively coupled to a coil 18 and together with the latter and condenser 3 provides for high frequency operation of the oscillator. The cathode 88 is connected through the inductance coil 19 to ground G. Screen grid 88 is connected through a condenser 80 to ground G and is also connected through a resistance 8I to the positive terminal of the D. C. voltage supply means 8, the negative terminal of which is connectedto ground G. As shown, the D. C. voltagesupply means includes a full wave rectifier tube 82 and a filter indicated generally at 83 inaddition to the transformer 1I. Rectifier tube 82 includes a pair of anodes and afllament type cathode which hasits' terminals connected to the low voltage transformer secondary winding 14. One end terminal of the high voltage secondary winding 13 isconnected to one anode of rectifier 82 and the other anode thereof is connected to the other end terminal of the winding 13. The center tap on the high voltage secondary winding 13 is connected toground G and constitutes the negative terminal of the D. C. voltage supply means. The filament of the rectifier tube 82 comprises the positive terminal of the D. C. voltage supply means and is connected through suitable inductances 84 provided in the filter 83 to the positive output terminal of the D. C. voltage supply means 5. The filter 83 is alsoprovided-with suitable condensers 85, as shown.

A resistance 88 and a condenser 81 are also provided for line voltage compensation purposes to the end that the frequency of oscillation of the oscillator 4 will remain" constant regardless of line voltage variations.- Anode 84 is connectedthrough axresistance 88 to the point of connectionv of resistance 88 and condenser 81. The suppressor grid 85 of the "tube 83 is connected to-gro'und G and serves the usual purpose of decreasing secondary'emission from the anode 84.

The oscillating circuitofthe o:cl1lator 4 includes the control grid circuit of which the parallel network including {the tuning condenser 3 forms a part, and-also includes the screen grid which, as previously noted, may be in theregion from 1450 to 1000 kilocycles. The anode .84 of the tube 83 v is electron coupled to the screen grid 88. and accordingly the high frequency oscillating currents conducted through thescreen-grid circuit are operative to cause the voltage of the anode 84 to oscillate at the same high frequency.

The anode or output circuit of the oscillator 4.

is shown as being directly coupled to the receiver 1 by means of a. condenser 88' and the transmission line 8. While the anode or output circuit of the oscillator 4 has been so shown, it will be understood that stages of amplification and isolation and an impedance matching network may be employed, if desired. Moreover, means for wireless transmission to the receiver 1 may also be provided in the well known and conventional manner, if desired,

Oscillator 8 contained in the receiver 1 maybe and has been shown as being identical to the oscillator 4 and includes a pentode tube 90 which may be of the commercially available type 6SJ'1. The tube 90 includes an anode 9|, a suppressor grid 92, a screen grid 93, a control grid 94, a cathode and heater filament 98. Heater filament 98 is connected to and receives energizing current from the secondary winding 91 of a transformer 98 located in the D. C. power supply means 8a. The transformer 98 includes a primary winding 99 having its terminals connected through the switch 54 to the supply lines L and L", and also includes a center tapped hignvoltage secondary winding I00 and a low voltage secondary winding IOI in addition to the low voltage secondary winding 91.

As shown, the D. C. supply means 8a is identical to the D. C. supply means 5 and includes a full wave rectifier tube I03'and a filter designated generally at I04 and comprising suitabl inductance coils I05 and suitable condensers I08. .The negative terminal of the D. C. supply means 8a is connected to the center tap of the high voltage secondary winding I00 and the positive terminal thereof is connected to the filament of the rectifier tube I03. A voltage divider resistance I02 provided with terminals designated a, b, c, d and e is connected between the positlveand negative output terminals of the filter I04; Terminal dis connected directly to ground G.

For the purpose of providing compensation for line voltag variations so that line voltage changes produce no significant change in the frequency of oscillation of the oscillator 8, a resistance I01 and a condenser I 08 are connected between the positive terminal-a and grounded terminal d. The point of connection of the resistance I01 and condenser I08 is connected through a resistance I09 to the anode 9|,and the cathode 95 of tube 90 is connected through an inductance coil IIO to the grounded terminal d on'the voltage divider.

Screen grid voltage is supplied to the oscillator tube 90 from the divider resistance I02 through a the grounded point d. Suppressor grid 92 is directly connected to ground G and Is provided for decreasing secondary emission from the anode N. A condenser 22' connects the screen grid 22 to ground G.

Control grid 24 is connected through a resistanceli2togroundGandisalsoconnected through a condenser II2 to one terminal of a parallel circuit including the retuning means or variable tuning condenser 2 in one branch and an inductance coil H4 in the other branch. The inductance coll H4 is inductively coupled to the inductance coil IIO. If desired, a trimming condenser, not shown, may be connected in parallel with the condenser 2 and inductance coil II4 for providing a fine adjustment of the zero setting the instrument pen and pointer.

The screen and control grid circuits of the tube 22 are inductively coupled'by the inductance coils H2 and H4 and are so arranged as to provide for high frequency operation over a range of frequencies in the region, for example, from 1000 to 000 kilocycles. Anode 2i of the tube 20 is electron coupled to the screen. grid 22 so that the high frequency oscillating currents flowing through the screen grid circuit may cause the voltage of the anode 2i to oscillate at the same high frequency.

The anode or output circuit of the oscillator 2 is coupled by means of a condenser III to an input circuit of the frequency mixer I and the transmission line 0 is also coupled to an input circuit of the frequency mixer I2. As shown, the frequency mixer I0 includes a multi-grid tube I I2 having an anode I I1. suppressor grid I I2, first and second screen grids Ill and I20, first and second control grids HI and I22, a cathode I22 and a heater filament I24. The heater filament I24 is connected to and'receives energizing current from the low voltage transformer secondary winding 21. The first control grid I2I is connected by the transmission line 2 and condenser 22 to the anode 04 of the transmitter oscillator tube 22 and is also connected through a resist- Anode voltage is supplied to the frequency mixer tube I I2 from the voltage divider resistance I22 through a circuit which may b traced from the positive terminal a through resistances I22 and I20 to the anode III, the cathode I22 and the parallel connected resistance I22 and condenser I2I to grounded terminal d on the voltage divider. Resistance I29 and a condenser I2I connected between the point of connection of resistances I22 and I20 and ground G are employed to provide a radio frequency by-pass to ground to prevent the high frequency currents in the anode circuit of tube II2 from flowing to the D. C. voltage supply means 20. The suppressor grid H2 is directly connected to the cathode I22.

Screen grids H2 and I20 are connected together'and are supplied with voltage from the voltage divider resistance I02 through a circuit which may be traced from terminal a through a resistance I22 to the screen grids, cathode I22 and the parallel connected elements I 22 and I2! to the grounded terminal d. The screen grids are also connected through a condenser I22 to around G.

The frequency mixer I2 is provided for heterodyning the high frequency currents conveyed to the receiver 1 from the transmitter oscillator 4 and the high frequency oscillating currents created in the output circuit of the receiver oscillatorl. Aswllibeunderstoodbythoseskilled in the art, the current flow through the output -The buffer II includes a pentode tube I22 which may be of the commercially available type 68.17. The tube I22 includes an anode I21. a suppressor grid I22, a screen grid-I22, a control grid I40. a cathode HI and a heater filament I42.

Energizing voltage is supplied to the heater filament I42 from the low voltage transformer secondary winding 21.

The control grid I42 is connected to the point of engagement of the coupling condenser I24 and the resistance I20 and is connected through the resistance I20 and a parallel connected cathode bias resistance I42 and condenser, I44 to the cathode I4I. According to one embodiment of the present invention, the coupling condenser I24 and resistance I22 are so chosen as to provide optimum transmission of the current com .ponent in the output circuit of the frequency mixer I0 having a frequency equal to the differ-- ence of the frequencies of the oscillators. 4 and 2.

In another embodiment transmission. of the current component having a; frequency equal to the sum of the frequencies of the oscillator's 4 and 2 is provided. If desiredpafilter may be inserted between the output circuit of the. frequency mixer I2 and the input'circuit of the buffer II for insuring that only the desired frej quencycomponent derived from the oscillators '4 and 2 is impressed on the input circuit of the buffer I I. 1

- Anode voltage is supplied to the buffer II from the voltage divider resistance I22 through a circuit which may be traced from the terminal I: on the voltage divider resistance through a parallel circuit including a condenser I40 in one branch ,and the primary winding I42 of an intermediate frequency transformer I41 in the other branch to the anode I21, the cathode "I and the paral- -lel connected resistance I42 and condenser I44 to the grounded terminal d. The suppressor grid I22 is directly connected to the cathode I4I.

Screen grid voltage is supplied to the tube I20 from the divider resistance I22 through a circuit which may be traced from the terminal b through a resistance I42 to the screen grid I22, the oathode I4I and the parallel connected resistance I42 and condenser I44 to the grounded terminal d. A condenser I42 is connected between the terminal b and ground G for filtering the voltage impressed on the screen grid I22. The screen grid I22 also is connected directly by a condenser I00 to ground G.

The frequency discriminator I2 is of the socalled balanced type and includes the intermediate frequency transformer I41 and a pair of diode rectifiers III and I02 which desirably may be contained within a single envelope and for l3 example may comprise the diode elements of a commercially available type 6H6 tube. The intermediatefrequency transformer I41 includes a split secondary winding in addition to the prialso to the upper terminal off-the primary winding I46. That center tap is also connected to the point of engagement of a pair of resistances I56 and I51 by means of a conductor I58.

As shown, the diode I5I includes an anode I59, a cathode I60 and a heater filament I6I, and the diode I52 includes an anode I62, a cathode I63 and a heater filament I54. The heater filaments are connected in series and are supplied with energizing current from the transformer secondary winding 91. Cathode I60 is connected through resistance I56 to the center tap of the split secondary winding and cathode I63 is connected through the resistance I51 to the said center tap. The anode I59 is connected to the end terminal of the split secondary winding section I53, and the anode I62 is connected to the end terminal of the split secondary winding section I54. A condenser I65 is connected across the terminals of the split secondary winding for tuning the latter to the center frequency about which the effective component of the oscillating output current of the frequency mixer I0 is adapted to be varied. On the assumption that the condenser I34 and resistance I35 are so chosen as to provide optimum transmission to the input circuit of the frequency discriminator of the oscillating current component in the output circuit of the frequency mixer I0 having a frequency equal to the difference of the frequencies of oscillation of the oscillators 4 and 8, the condenser I65 is so chosen in relation to the discriminator constants as to tune the split secondary winding of the frequency discriminator I2 to that difference frequency, namely, 450 kilocycles per second. When condenser I34 and resistance I35 are so chosen as to provide optimum transmission of the oscillating current component in the output circuit of the frequency mixer I0 having a frequency equal to the sum of. the frequencies of oscillation of the oscillators 4 and 8 to the input circuit of the discriminator, the condenser I65 is so chosen as to tune the discriminator to that frequency. A condenser I66 is connected in parallel with both of the resistances I56 and I51. The blocking condenser I55 and the condenser I66 are so selected as to present low impedance to the high frequency oscillating current flow through them. The condenser I45 and the transformer primary winding I46 are so selected as collectively to provide high impedance in order to produce a large output signal from the discriminator. Preferably, the primary winding I46 is tuned to the same frequency as that to which the split secondary winding is tuned.

When the frequency of the oscillating current applied to the transformer primary winding I46 cally in Fig. 4 wherein the vector Em represents the voltage applied to the primary winding I46 and the vectors E153 and E154, respectively, represent the voltages produced across the split secondary windingsections I53 and I54. The phenomenon giving rise to the 90 phase shift between the primary and secondary voltages is one known in the art and therefore needs no explanation herein.

The secondary winding sections I53 and I54 are so wound on the transformer I41 that the voltage appearing across the winding I53 is 180" out of phase with the voltage produced across the winding I54. This relationship also is shown in Fig. 4. The voltage produced across section I53 is impressed on the circuit including the diode rectifler I5I and the resistance I56 while the voltage developed across the section I54 is im pressed on the circuit including the diode I52 and the resistance-I51. Superimposed on each of these voltages is the voltage produced across the primary winding I46. Since the upper terminal of the primary winding I46 is connected through the blocking condenser I55 to the center tap of the split secondary winding and the lower terminal of the winding I46 is connected through condenser I49 to ground G, and since the remote ends of the resistances I56 and I51 are each connected to ground G through paths presenting low impedance to the high frequency currents impressed on the discriminator, the primary voltage is superimposed on the voltage produced across section I53 on the circuit including diode I5I and resistance I56 and also is superimposed on the voltage produced across section I54 on the circuit including diode I52. Thus, the

resultant voltage impressed on the circuit including the diode I5I is the vector sum of the I primary voltage Em and the secondary voltage E153, which vector sum is represented in Fig. 4 by the vector Er. The vector E.- in Fig. 4 represents applied to the primary winding I46 and the voltages appearing across the secondary winding sections I53 and I54 exists only when the applied frequency to the primary winding I46 is the value to which both the primary and the split secondary windings are resonant. Upon departure of the applied frequency from this value, the voltages produced across the secondary winding sections I53 and I54 also depart from the 90 phase relationship with the voltage applied to the primary winding, as may be seen by reference to the vectors E'm and E'154 in Fig. 4. For example, upon increase in the applied frequency from the value to which the secondary winding is resonant, the phase displacement between the voltage produced across the secondary winding section I53 and the applied primary voltage decreases toward zero while the phase displacement between the voltage produced across the secondary winding sec tion I54 and the primary winding increases toward Upon decrease in the applied frequency the opposite condition exists, that is to say, the phase displacementbetween the vectors E15: and Em in Fig. 4 increases toward 180 while the displacement between the vectors Em and Em decreases toward zero.

When the applied frequency to the primary winding I48 deviates slightly, for example, increases from the value to which the secondary winding is tuned, the resultant voltage applied to the diode I52 will decrease as shown by the vector E'ar while the resultant voltage supplied to the other diode I5I will increase as is indicated by the vector E". Upon greater deviation in the applied frequency in the same direction the resultant voitage applied to the first mentioned diode I52 will continue to decrease while the voltage applied to the second mentioned diode I5I will increase-to a maximum value and upon still greater deviation will begin to decrease as may be seen by reference to Fig. 5 wherein the curve er represents the manner in which the resultant voltage applied to the diode I5I changes upon variation in the applied frequency and the curve e'r represents the manner in which the resuitant voltage applied to the diode I52 simultaneously changes.

By referring to Fig. 5, it will be noted that the resultant voltage er applied to the diode I5I will increase initially as the applied frequency increases from the value to which the secondary winding is resonant until it reaches a maximum value after which it will begin to decrease as the applied frequency is changed further in the same direction. The resultant voltage then applied to the other diode I52 will decrease and continue gradually to decrease as the applied frequency deviates further from the resonant value. As a result of this action the voltage drop produced across the resistance I56 will be increased while that produced across the resistance I51 will be decreased.

Upon deviation in the frequency of oscillation of the current applied to the discriminator in the opposite direction from the value to which the discriminator is tuned, the resultant voltage applied to the diode I5I will decrease while the voltage applied to the diode I52 will increase to a maximum value, following which the latter voltage will also begin to decrease. Because of this action the voltage drop produced across the resistance I51 will be increased while the voltage drop produced across the resistance I56 will be decreased.

The manner in which the voltage drops developed across the resistances I56 and I51 change with variation in the applied frequency is illustrated in Fig. 5 by the curve E0. At the point of intersection of the curve E; with the .r--.r axis, the voltage drops produced across the resistances I56 and I51 are equal. A portion of the curve E0 to the right of the 11-11 axis represents the difference in the voltage drops across the resistances I56 and I51, the voltage drop across resistance I56 being the greater and occurring upon an increase in the applied frequency from the value to which the discriminator I2 is tuned, The portion of curve E0 at the left of the y--y axis represents the difference in magnitudes of the voltage drops across the resistances I56 and I51, the voltage drop across the resistance I51 being the greater and occurring upon a decrease in applied frequency.

In the arrangement of Fig. 3, there are two normal operating conditions in which the resultant of the voltages produced across the resistances I56 and I51 is zero. The first is that ocances I56 and I51 to pulsate upon deviation of the frequency of the oscilating currents applied to the discriminator from the value to which the latter is tuned. Further, the said resultant voltage is made to pulsate at the relatively low frequency of the voltage of the supply lines L and L" and is of one phase or of opposite phase relative to the supply line voltage depending upon the direction of deviation in the frequency of the applied oscillating currents from the value to which the discriminator is tuned.

To the attainment of this end the high frequency oscillating current output of the buffer II is substantially 100% square wave amplitude modulated at the relatively low frequency of the voltage of the supply lines L and L" by means including the keyer I3. As shown, the keyer I3 includes a pentcde tube I61 which may be of the commercially available type GSJ'I including an anode I68, a suppresso grid I69, a screen grid I10, a control grid IN, a cathcde I12 and a heater filament I13. Energizing current is supplied to the heater filament from the transformer secondary winding 91.

Anode voltage is supplied to the tube I81 from the voltage divider resistance I02 through a circuit which may be. traced from the terminal b through resistance I48 and a resistance I14 to the anode I60, cathode I12 and a cathode bias resistance I15 to the negative terminal e cf the voltage divider resistance I02. It is noted that the condenser I49 also serves to provide a radio frequency by-pass to ground in the anode circuit of tube I36. Suppressor grid I09 is directly connected to the cathode I12 for the purpose of minimizing secondary emission from the anode I68.

Voltage is supplied to the screen grid I10 from the voltage divider resistance I02 through a circuit which may be traced from the terminal 0 to the screen grid I10, cathode I12 and bias resistance I15 to the negative terminal e on the voltage divider I02.

Control grid "I is connected through a pair of series connected resistances I16 and I11 to the negative terminal of bias resistan e I15, the other terminal of which is connected to the cathode I12. Alternating voltage of the same relatively low frequency as that supplied by the supply lines L and L" is impressed on the resistance I 11 from the secondary winding I18 of a transformer I19 havinga line voltage primary winding I80. The terminals of the line voltage primary winding I are connected to the supply lines L and L", preferably through a switch, not shown but which may be the switch 54. The transformer I19 is also provided with a center tapped secondary winding I8I which is employed for t e purpose of supplying energizing current to the power amplifier I6 and also to the reversible motor I5.

The cir uit path through which the alternating current is impressed on the resistance I11 may be traced from the lower terminal of resistance I11 through a condenser I 82 to ground G, to the right end terminal or the transformer secondary winding I18 and from the other terminal of the latter to the upper end of the resistance I11. Alternating current flow through the resistance I11 pro- 'posite pole pieces.

duces a voltage drop. across it which is operative l to make the keyer tube I31 conductive and nonconductiveat the frequency of the voltage .of the supply lines L'and L". This causes the voltage of the anode I33 to fluctuate with an approximately square wave form between, a value approximating the potential of the terminal b on the voltage divider resistance I02 and a value approximatingthe potential of the terminal ethereon. Since the screen grid I33 of the tube I38 is connected through resistance I14 to the anode I33 of tube I31, the screen grid I39 is made to fluctuate in a corresponding manner. Accordingly, the tube I36 is made alternately conductive and substantially non-conductive at the relatively low frequency of the supply lines L and L".

Consequently. high frequency oscillating currents of substantially constant amplitude flow in the output circuit oi the buffer II and. are applied to the frequency discriminator I2 only during the intervals in which the tube 13s is conductive.

During the alternate intervals when the tube I36 is non-conductive no high frequency currents are applied to the discriminator.

From the foregoing it will be apparent that the resultant of the potentials produced across the resistances I56 and IE1 and appearing between the terminals I33 and I33 is zero when the frequency of oscillation'of the high frequency currents applied to the discriminator I2 is the value to which the discriminator is tuned and that upon towhlch the discriminator is tuned. Moreover,

since the high frequency oscillating currents applied to the discriminator I2 are amplitude modulated by the keyer I3 with an approximately square wave form at the frequency of the voltage supplied by the supply lines L' and L", the undulating voltage produced between the terminals I33 and I 83 is also substantially of a square wave form and of the same frequency as is shown in Fig. 6, wherein the curve Es represents the supply line voltage while the curves E1 and Ed respectively represent in-phase and out of phase discriminator output voltages.

Those skilled in the art will recognize that the invention in its practical application is not restricted to the use of a frequency discriminator I2 of the type disclosed and that other types, particularly those conventionally employed for automatic frequency control and frequency modulation detection in radio broadcast receivers, may be employed equally as well.

Asnoted hereinbefore, the reversible motor I5, as seen in Fig. 1, is provided with a stator 23 having 4 pole pieces which are physically spaced apart by 90 and also includes a rotor 30. It will be evident that more than 4 pole pieces may be provided on the motor I5 if desired. The power winding 3| is wrapped around two of the opposite pole pieces of the stator 23 and the control winding 32 is wrapped around the remaining two op- When only the power winding 3| is energized. the rotor 30 is not urged to rotation in either direction and remains station- 'ary. The rotor 33 is --tion, when the control winding 32 is energized and the voltage and current through it lead the voltage and current, respectively, in the power winding 3|. When the voltage and current in the control winding 32 lag the voltage and current, respectively, in the power winding 3|, the rotor 30 rotates in the opposite direction.

The motor II is preferably so constructed that the control winding 32 has a high impedance to match the impedance of theanode circuit of the power amplifierifi when the rotor 33 is rotating at full speed. By providing a power winding 3| having high impedance, increased emciency of operation is obtained. Preferably the control and power windings of the motor have a high ratio of inductive reactance to resistance, for example from 6 to l'to 8 to 1, at the frequency of the alternating current supplied" by the lines L and L". This provides for maximum power during running with the least amount of heating and also provides a low impedance path in the control winding 32 for anti-hunting control purposes. By so designing the motor, reduction in heating thereof during its stalled condition is also obtained.

As may be seen by reference to Fig. 3. energizing current is supplied to the power winding 3| from the alternating current supply lines L and L" through a circuitwhich may be traced from the alternating current supply line L through the power winding 3| and a condenser I to the supply line L". The condenser IE5 is so chosen with respect to the inductance of the power winding 3| as to provide a substantially series resonant circuit when the rotor 3|] is rotating at approximately full speed. Since the power winding circuit is resonant, its total impedance is substantially equal to the resistance of the power wind ing 3|. This resistance is relatively low, and therefore, a large current flow through the power winding is made possible, resulting in the production of maximum power and torque by the motor.

" Due to the series resonant circuit also the current flow through the power winding 3| is substantially in phase with the supply line voltage. The voltage produced across the power winding 3|, however, leads the current flow by substantially because of the inductance of the power winding.

When the rotor 30 is operating at substantially maximum speed the apparent inductance of the power winding 3| is a maximum whereupon the series resonant circuit is resonant to the applied alternating current from the supply lines L' and L". As the speedof rotation of the rotor 33 decreases the apparent inductance of the power winding 3| decreases, and therefore, disturbs to some degree the resonant condition. This'causes a slight phase shift in the current through and the voltage produced across the power winding, the voltage shifting somewhat more than the current and consequently reducing thepower loss in the power winding. In addition, the change from the resonant condition causes areduction in the current flow through the power winding and because of the decrease in apparent inductance, the voltage acrossthe power winding. 3| also decreases. This produces a further reduction of power loss in the'power windings. As a result, there is a substantial reduction of heating of the power winding whenthe rotor 33 is at rest. h H

As shown in Figs. .2 and 3, the undulating voltcomprise one triode section of a commercially available 7N7 tube or any other tube having similar characteristics. The tube I88 includes an anode I81, a control grid I88, a cathode I88 l anda heater filament I88, to the latter of which energizing current is supplied from the transformer secondary winding 81.

The input circuit of the triode I88 is controlled in accordance with the undulating voltage drop produced between the discriminator output terminals I88. and I88 and to this end the control grid I88 is connected through a condenser I8I to the terminal I88 and the terminal I88 is connected directly to the cathode I88. A resistance I82'is also connectedbetween the control grid I88 and the'cathode I88. The cathode I88 is connected directly to ground G. It will be apparent that if desired the condenser I8I may be eliminatedand direct coupling employed between the output terminals of the discriminator I2 and the input circuit of the tube I88. In some cases it is preferable to employ direct coupling for the purpose of minimizing distortion of the square wave character of the discriminator output voltage.

Anode voltage is supplied to the triode I88 from the voltage divider resistance I82 through a circuit which may be traced from the terminal b through a pair of series connected resistances I88 and I88 to the anode I81 and the cathode I88 to the'g'rounded terminal (I. A condenser I88 is also connected between the point of engagement of resistances I88 and I88 and the grounded terminal 01 for the purpom of providing additional filtering of the anode voltage.

The power amplifier I8 includes in addition to the transformer I" a twin triode tube I88 which may be of the commercially available type 7N7, one triode including an anode I81, a control grid I88, a cathode I88 and a heater filament 288, while the other triode includes an anode 28I, a control grid 282, a cathode 288 and a heater filament 288. Energizing current is supplied to each of the heater filaments 288 and 288 from the transformer secondary winding 81.

The control grids I88 and 282 are directly connected to each other and to a contact 288 which is in engagement with and is ad ustable along the length of a resistance 288. The resistance 288 has one end terminal connected throu h a condenser 281 to the anode I81 of the voltage amplifier tube I88 and h s its other end terminal connected to ground G. The resistance 288 and conden er 281 are pro ided for impressin the fluctuatin or undulating com onent of voltage roduced in the o t ut circ it of the voltage amplifier I8 on the in ut circuit of the power amplifier I8 while preventing the direct current component of the current flowing through the anode circuit of the tube I88 from being impressed on the input circuit of the power amplifier I8. Since the power amplifier control rids I88 and 282 are connected to ether, the output voltage from the voltage amplifier I8 is impressed simultaneously and equally on both of the in ut circuits of the triodes contained in tube I88. The adjustable resistance 288 is provided to facilitate adjustment in the gain of the power amplifier I8.

Anode voltage is supplied to the triodes of the power amplifier I8 from the split secondary winding III on the transformer I18. To this end the anode I8! is connected to the left end terminal oi the winding I8I while the anode 28I is connected to the right end terminal of that winding. The cathodes I88 and 288 are connected together and through a biasing resistance 288 to ground G. The center tap on the split secondary winding In is connected through the control winding 82 0f the motor I8 to ground 0 to which the cathodes I88 and 288 are also connected by the biasing resistance 288.

Power is supplied to the motor control winding 82 from the split secondary winding I" through the anode circuits Just traced of the tube I88. A condenser 288 is connected in peralq lel with the control winding 82 and is so selected as to provide a parallel resonant circuit during both the stalled and running conditions of the motor. This parallel resonant circuit presents a relatively high external impedance and a relatively low internal impedance. The relatively high external impedance of the parallel resonant circuit matches the impedance of the anode circuits of the power amplifier triodes, and therefore, provides for optimum conditions of operation. The relatively low internal circuit impedance of the control winding 82 and the condenser 288 approximates the actual resistance of the control winding 82, and since this resistance is relatively low, the impedance of the internal circuit is also relatively low, making possible a large current fiow through the control winding.

The sections of the split transformer secondary winding "I are so wound on the transformer I18 that the anode I81 of the power amplifier tube I88 is driven positive during one half cycle or the alternating current supply voltage. For convenience of CAI-81811381011, this half cycle is hereinafter referred to as the first half cycle. The anode 28I of the other triode is driven positive during the opposite or second half cycle. In the first half cycle the anode 28I is negative with respect to the potent al of the center tap. but in the second half cycle the anode 28I becomes positive while the anode I81 becomes negative with respect to the potential of the center tap. The voltage on the anode I81 accordingly may be assumed to increase and decrease in phase with the supply line voltage while the voltage on the anode 28I increases and decreases 188 out of phase with the su ply line voltage. This relationship always remains substantially the same.

While the foregoin description of the motor drive ap aratus includ ng the voltage amplifier I 8 and the power amplifier I8 and its operation is believed sufil ient for the present purposes, reference is made to t e aforement oned Wills patent for a more detailed description thereof.

When the rate of fluid fiow through the conduit I remains at the desir d value the frequency of oscillation of the high frequency current output from the freouency mixer I8 is the frequency value to which the discriminator I2 is balanced. Accordin ly. the cutout terminals I88 and 88 of the fre uency discriminator are maintained at the s me pote tial during both half cycles of the volts ge sup lied in the sup ly lines L' and L" and the motor I8 is not energised for rotation in either direction and remains stationary. v,

Upon an increase in the rate of fiuid fiow throu h the cond it I the man meter 2 operates the detuning condenser 8 to make an adjustment of the condenser plate 21 in the clockwise direc- I output current from the frequency mixer III which is applied-to the input terminals of the frequency discriminator i2. As a result, an undulating voltage in phase with the voltage of the supply lines L and L" appears between the discriminator output terminals I88 and I84. This undulating voltage is amplified by the voltage amplifier l4 and impressed on the input circuit of the power amplifier I8 for selectively energizing the motor II for rotation in one direction. The motor I! then operates through the cable drive mechanism to adjust the movable condenser plates 48 of the retuning condenser 8 in the frequency determining circuit of the oscillator 8 in the proper direction to cause the difference in frequency of the high frequency oscillating currents from the oscillators 4 and 8 and flowing in the output circuit of the frequency mixer I 8 to be restored to the frequency value to which the frequency discriminator i2 is tuned. When the condenser 8 has been so adjusted the motor I! is deenergized for rotation and quickly comes to rest.

It is noted that when the discriminator I2 is tuned to the sum of the frequencies of the oscillators 4 and 8, the motor I! operates the retuninl condenser 8 in the proper direction as required to cause a decrease in frequency of oscillator 8 exactly correspondingflto the increase in frequency of oscillator 4 caused by the adjustment of condenser 8.

Upon a decrease in the rate of fluid flow through the conduit l the manometer 2 operates the detuning condenser 3 in the opposite direction to increase its capacity. This produces a decrease in the frequency of oscillation of the transmitter oscillator 4 and consequent y a decrease in the frequency of oscillation of the oscillating current in the output of the frequency mixer l8. As a result, an undulating voltage of opposite phase with respect to the voltage supplied by the supply lines L' and L" is produced between the discriminator output terminals I88 and I84. The motor I! is then energized for rotation in the opposite direction to effect an adjustment of the retuning condenser 9 in the reverse direction to .cause the frequency of oscillation of the oscillating current in the output circuit of the frequency mixer ill to be restored to the value to which the frequency discriminator I2 is tuned. When such adjustment has been given the condenser 9, the energizing current urging the motor IE to rotation is reduced to zero and the motor l5 quickly comes to rest. I

Thus, the motor l5 operates in one direction or the other accordingly as the frequency of oscillation of the current flow in the output circuit of the frequency mixer ill increases or decreases from the value to which the discriminator I2 is tuned. Moreover, the speed of the motor IS in either direction is directly dependent, within a predetermined range, upon the magnitude of the change in the said frequency of oscillation.

As those skilled in the art will understand, my

present invention in its practical application is not restricted to the use of a variable condenser for retuning the receiver oscillator 8. For example, the said detuning and retuning adjustments of oscillators 4 and 8 may be effected solely by means of variable inductive reactance elements or by a combination of capacitive and inductive reactance elements. When inductive reactance elements are employed for accomplishing the detuning and retuning adjustments of the oscillators, it may be desirable in some cases to provide inductive reactance elements of the type having high frequency cores in order to produce a relatively large change in frequency of oscillation for a small movement of the actuating element. y

In Figs. 7 through 11 I have illustrated more or less diagrammatically modifications of the arrangement shown in Figs. 2 and 3 which differ from the latter arrangement by the application of direct oscillator amplitude modulation or keying thus permitting the keyer l3 to be dispensed with, and therefore, permitting an appreciable reduction in the amount of equipment involved. Figs. 7 and 8 collectively illustrate one such modification, Figs. 9 and 10 collectively illustrate another modlfication, and Fig. 11 illustrates a third modification. Each of these modifications differs from the arrangement of Figs. 2 and 3 in that the frequency discriminator I2 is tuned to the sum of the frequencies of the oscillating currents generated by the oscillators 4 and 8 rather than to the diflerence in those frequencies. It is noted, however, that if desired, the frequency discriminator of the arrangement of Fig. 11 may also 8 for detuning the transmitter oscillator '4 in respouse to a change in the rate of fluid flow through the conduit l or in the particular variable condition under measurement and also is not restricted to the use of a variable condenser 9 be tuned to the difference between the frequencies of the transmitter and receiver oscillators. It is noted further that the frequency discriminator in the modifications of Figs. '7 through 10 may be tuned to the difference between the frequencies of the transmitter'and receiver oscillators provided that a suitable filter is interposed between the frequency mixer I8 and the frequency discriminator i2 to prevent oscillating currents of the relatively high frequency produced by oscillators 4 and 8 from being impressed on the discriminator H. For convenience of illustration, parts in Figs. 7 through 11 corresponding to parts in Figs. 2 and 3 have been identified by the same reference numerals.

The modification of Figs. 7 and 8, as may readily be seen by reference to the block diagram of Fig, 'l, differs in construction from the arrangement described in Figs. 2 and 3 by the provision of alternating current power supply means indicated by the reference numeral 5a in lieu of the direct current power supply means 5 shown in Figs. 2 and 3. The alternating current power supply means in provides alternating current anode voltage for the oscillator 4, and consequently, high frequency oscillating currents flow in the output circuit of the oscillator 4 only during the alternate half cycles of the alternating voltage provided by the alternating current power supply means when the anode 64 of the oscillator tube 83 is 'positive with respect to the potential of the cathode 88. During the other half cycle when the anode 84 is negative with respect to the cathode potential, no currents flow in the output circuit of the oscillator.

According to this modification of my invention, the alternating current supplied by the altemating current power supply means 50. is preferably of the same frequency as that of the alternating current supplied to the receiver 1 by the supply,

assume may desirably be also supplied by the supply lines L and L". It is not essential, however, that the' transmitter and the receiver be both energized from the same alternating current supply. lines and it is sufficient if this transmitterand receiver are both energized with alternating current of the same frequency. This feature is of importance when the modification of Figs. 7 and 8 is employed in telemetering or remote control applications. In such applications the transmitter and receiver may be so remotely located with respect to each other that it is not practically feasible to supply alternating current to both units from the same power supply lines. For convenience of illustration, however, in Figs. 7 and 8 the transmitter and receiver have been shown as being supplied with alternating current from the same supply lines.

Referring to Fig. 8 it willbe noted that the alternating current power supply means id for supplying alternating anode voltage to the oscillator tube 60 includes a gaseous discharge tube designated by the reference numeral 210 and a pair of resistances 2H and 2I2. The resistance 2I2 is connected in parallel with the tube 2I0 and the resistance 2 connects the parallel network to the supply lines L and L". Tube H is provided with an anode 2I3 and a cathode 2, the anode 2I3 being connected to ground G and also to the supply line L while the cathode 2 is connected through the resistance 2 to the supply line L". The gaseous discharge tube 2I0 operates conjointly with the resistance 2I2 to produce a pulsating potential of substantially square wave form and of the same frequency as the voltage of the supply lines L' and L" across the resistance 2 I 2. That pulsating voltage across the resistance 2I2 is impressed on the anode and screen circuits of the oscillator tube 00, which circuits are identical to the corresponding anode and screen circuits of the oscillator 0 shown in detail in Fig. 3. When the anode and screen circuits of the oscillator 4 are so energized, high frequency oscillating currents flow in the anode circuit during the intervals when the anode 00 and the screen 00 are positive in potential with respect to the cathode 00 and during the alternate intervals no high frequency currents fiow through the anode circuit of the oscillator 0. Accordingly, high frequency oscillating currents are impressed on the transmission line 0 during only the regularly recurring intervals when the anode 04 and the screen 60 are positive, those intervals corresponding to one half cycle of the alternating current supply lines L and L As shown, the alternating current supply means,

0a also includes a transformer Ila for supplying energizing current to the heater filament 09 of the oscillator tube 03. Transformer Ila includes a line voltage primary winding 'II'b having its terminals connected to the supply lines L' and L" and is provided with a secondary winding I Ic identical to the receiver 1 of Fig. 3 except that the buffer II and the keyer I3 have been eliminated and that an additional stage of amplification has been provided in the voltage amplifier I4.

As shown, anode and screen voltages are supplied to the receiver oscillator 0, the frequency 24 mixer I0, a nd the voltage amplifier I0 from. D. C. power supply means 00 which may be identical to the D. C. power supply means 00 of Fig. 3 except that a voltage divider resistance I02 having only terminals a, f and e is employed in lieu, of the voltage divider resistance I02. The negative terminal e on the divider resistance I02. is

directly connectedto ground G. Anode and screen voltages are supplied to the receiver oscillator 0 and the frequency-mixer I0 from the posi tive terminal a.

Anode voltage is supplied to the voltage amplifier tube I00 from the terminal! on the voltage divider resistance I02 through a resistance III and through the resistances I00 and I04 to the anode I01. As shown, the output circuit of the voltage amplifier tube I 00 is coupled to the input circuit of a'voltage amplifier tube I00, the

latter of which may be a triode of the same type,

as the triode I00. For example, the triodes I00 and I00 may each comprise a section of the commercially available type 7N7 tube. The triodel86' includes an anode I01, a control grid I00, a cathode I00 and a heater filament I00. Energizing current is supplied to the filament I00 from the transformer secondary winding 01.

Anode voltage is supplied the triode I 00' through a circuit which may be traced from the terminal I on the voltage divider resistance through resistance 2I5 and a resistance 2I0 to the anode I 01 and the cathode I00 to ground G and thereby to the negative terminal e of the voltage divider resistance I02. -A condenser 2" is connected between ground G and the point of engagement of resistances 2 I 0 and U0 for providing additional filtering of the voltage inrpressed on the anode I01.

The output circuit of the triode I00 is coupled to the input circuit of the triode I00 by means of the condenser 201 and a resistance 2". Specifically, the anode I01 is connected by the condenser 201 to thecontrol grid I00 of the triode anode circuit of' the triode I00 is impressed by means of a condenser 2l0 and the potentiometer resistance 200 and associated contact 200 on the input circuits of the triodes included in the tube I of the power amplifier I0.

The operation of this modification of my invention will now be described. As has been noted hereinbefore In connection with the description of the arrangement of Fig. 3, there are two conditions of operation of the frequency discriminator I2 in which the voltage output from the' discriminator is substantially zero. The first of these conditions is that in which nohigh frequency currents are impressed on the input circuit of the frequency discriminator and the second condition is that in which the high frequency currents impressed on the input circuit of the discriminator are of the frequency value to which the discriminator is tuned. As those skilled in the art will understand, there also is a third condition of operation in which the output voltage from the discriminator is zero, namely that which exists when the high frequency currents impressed on the input circuit of the frequency discriminator have a frequency value which is widely displaced from the frequency a cane-1a value to which the discriminator is tuned. This characteristic of the operation of the frequency discriminator I2 is taken advantage of in the modification of .my invention shown in Fig. 8 in order t derive an undulating voltage between the discriminator output terminals I88 and I84 of the same frequency as the voltage of the supply llnes L and L" and in phase or 188 out of phase therewith.

During the first half cycles when positive'anode and screen voltages are supplied to the oscillator tube'fl, hereinafter termed the-operative half cycles, high frequency oscillating currents are impressed over the transmission line 8 on the frequency mixer I8 and during those same intervals high frequency oscillating currents are impressed on the frequency mixer I8 by the receiver oscillator 8. When the system is balanced the sum of the two high frequency-oscillating currents i equal to the frequency value to which the frequency discriminator I2 is tuned, and consequently, substantially zero output voltage is produced between the output terminals I88 and I84 of the discriminator. During the alternate half cycles no high frequency oscillating currents are impressed on the frequency mixer I8 from the transmitter oscillator 4, and there-' fore, the high frequency currents flowing in the output circuit of the frequency mixer I8 and impressed on the input circuit of the frequency discriminator I2 are of the same frequency as the high frequency oscillating currents impressed on the input circuit of the frequency mixer I8?- by the receiver oscillator 8. This high frequency 2;-

oscillating current then impressed on the input circuit of the frequency discriminator "I2 is of a value which is widely different from the value to which the frequency discriminator is tuned, namely the sum of the receiver and transmitter oscillator frequencies, and accordingly, the voltage produced between the output terminals I88 and I84 of the discriminator will be substantially zero. This zero output voltage condition is always the same during the regularly recurring intervals when no high frequency oscillating currents are impressed on the frequency mixer I8 from the transmitter oscillator 4.

Consequently, when the sum of the high frequehcy oscillating currents produced by the transmitter oscillator 4 and the receiver oscillator 8 deviates from the value to which the frequency discriminator I2 is tuned, as upon variation in the adjustment of condenser 8, a unidirectional voltage of one polarity or the other depending on the direction of deviation is produced between the output terminals I83 and I84 of the discriminator I2 during the operative half cycles. During the other half cycles when high frequency oscillating currents from the oscillator 8 are alone impressed on the frequency mixer l8 by the receiver oscillator 8, substantially zero output voltage is obtained between the discriminator output terminals I88 and I 84. Thus, upon unbalance of the system a pulsating unidirectional voltage of one polarity or the other is produced between the discriminator output terminals I83 and I84. The pulsations in the unidirectional voltage produced between said output terminals are of the same frequency as the alternating voltage supplied by the supply lines L and L" and are of one phase or of opposite phase relatively thereto depending upon the direction of adjustment of the condenser 8 from the position in which zero output voltage is obtained between the discriminator output terminals I88 and I84 during the operative half cycles.

This pulsating or undulating voltage of one phase or of opposite phase is amplified by the voltage amplifier I4 and the amplified quantity is impressed on the power amplifier It for selectively controlling the rotation and the direction of rotation of the reversible motor I5. The operation of the motor I5 is utilized to effect the required adjustment of the retuning condenser 9 in the frequency determining circuit of the oscillator 8 needed to reduce the undulating voltage between the discriminator output terminals I83 and I84 to zero, and hence to rebalance the apparatus.

The modification of my invention shown in Figs. 9 and 10 differs from that shown in Figs. '7 and 8 only in that direct current voltage supply means 5 are provided at the transmitter and alternating current power supply means 8b are provided at the receiver and in that only one stage of amplification is provided in the voltage amplifier I4. I now prefer the modification of Figs. 9 and 10 over that shown in Figs. 7 and 8 in that the arrangement of Figs. 9 and 10 is entirely independent of frequency and phase.

shifts which may occur between the sources of alternating voltage provided at the transmitter and receiver.

As may be seen by reference to Figs. 9 and 18, the transmitter 4 and the D. C. power supply rneans 5 are identical to the correspondingly identified parts of Figs. 2 and 3. The receiver lb is'-identical to the receiver 1 of Figs. 2 and 3 with the exception that the keyer I3 is omitted and a gaseous discharge tube 22-8 and associated resistances 22I and 222 have been provided for supv plying alternating anode voltage to the receiver oscillator 8. The gaseous discharge tube 228 is provided with an anode 223 and a cathode 224, which elements are shunted by the resistance 222. The anode 223 is connected through the switch 54 to the supply line L' and the cathode 224 is cons nected through the resistance '2-2I and switch 84 to the supply line L". The gaseous discharge tube 228 together with the resistances MI and 222 operate to provide pulsating unidirectional voltage of substantially square wave form pulsating at the frequency of the supply lines L and L" to the anode and screen circuits of the oscillator 8. Unidirectional voltage is supplied to the frequency mixer I8 and to the voltage amplifier I4 from the D. C. supply means included in the supply means 8b.

It is noted that the anode and screen grid circuits of the frequency mixer I8 may be supplied with alternating or fluctuating energizing voltage of the same frequency as the voltage of the supply lines L and L, and for example, may be supplied with such energizing voltages from the tube 228 and resistance 222. When so energized current flows in the output circuit of the frequency mixer I8 only during the half cycle that the oscillator 8 produces high frequency currents, and as a consequence, with such an arrangement no high frequency currents are impressed on the input circuit of the discriminator I2 during the half cycles when the oscillator 8 is not operative and no discriminator output voltage is produced during those half cycles.

It .will be apparent that alternating or fluctuating anode and screen grid voltages may also be supplied to the frequency mixer I8 in the arrangement shown in Figs. 7 and 8 and so arranged that the frequency mixer tube H8 is con-i 

